1. Field of the Invention
The present invention relates generally to a spring-actuated electromagnetic brake having a noise suppressing device for suppressing a striking noise generated when a spring-loaded armature strikes against a lining on a brake plate upon engagement of the brake.
2. Description of the Related Art
FIGS. 6A and 7A show an example of conventionally known spring-actuated electromagnetic brakes having a noise suppressing device. The known electromagnetic brake includes a field 1 having a plurality of holes or recesses 1d' (one being shown) formed in an attracting surface onto which an armature 3 is attracted against the force of brake springs (not shown) when the field 1 is magnetized. A cylindrical noise-suppressing member 11' (FIG. 6B) made of rubber is disposed in each of the recesses 1d' in such a manner that when the brake is in the engaged state shown in FIG. 6A, the rubber noise-suppressing member 11' projects outward from the attracting surface, as better shown in FIG. 6B. The rubber noise-suppressing members 11' thus arranged can suppress a striking noise generated when the armature 3 is attracted onto the field 1 to thereby release the brake, as shown in FIG. 7A, upon excitation of an electromagnetic coil 2 to magnetize the field 1. When the brake is in the released state shown in FIG. 7A, there is a gap G between the armature 3 and a lining 5 on a brake plate 4. This means that when the brake is actuated again, the armature 3 is urged by the non-illustrated brake springs to move across the gap G and strike the lining 5. Upon striking, a sharp striking noise is emitted from the brake. The conventional spring-actuated electromagnetic brake has no function in reducing the level of striking noise generated when the spring-loaded armature 3 strikes against the lining 5 to engage the brake.
To lower such striking noise, it may be considered that the gap G be set small to reduce the striking distance of the armature 3 relative to the lining 5. In this case, however, there arises another problem that an extremely high degree of working accuracy is required for the manufacture of the field, armature, lining, brake plate and other parts of the brake.